The invention pertains to a sensor and a method for detecting an object or a thermal energy radiating substance provided partly on an object. In particular, this invention relates to the detection or monitoring of material dispensed onto a substrate, such as infrared monitoring of beads of adhesive material, such as but not limited to, the monitoring of beads of hot melt adhesive deposited on cartons or the like.
Methods for detecting the presence of an object and the length of the object, by moving the object or a sensor, have been carried out by using various sensors. For example, a limit switch-type sensor, a photoelectric sensor, an ultrasonic sensor, a color difference distinguishing sensor, and a proximity sensor have been used. These sensors have both advantages and disadvantages with regard to their use, performance, and cost features. In the field of applying a hot melt adhesive to a packaging material, attempts have been made to detect a heated material, such as a hot melt adhesive applied to an object, by providing two separate sensors for detecting the object and for detecting the heated material; such as an infrared sensor used as the sensor for detecting the heating material.
Up to now, the main problem with various sensors is their susceptibility to the effect of external disturbances. For example, noise or indirect energy from the surroundings that is close to the detection level of the sensor, often leads to erroneous detection. Furthermore, there is also a flaw in the response speed. For example, the response speed is limited to several tens of milliseconds in switch-type sensors and in proximity sensors, and a response speed of several milliseconds is the limit in a photoelectric sensor.
In order to detect whether or not the hot melt adhesive has been applied to a given location on the packaging material, one method that has been tried combines the signal from a sensor for detecting the packaging material and the signal from a sensor for detecting the hot melt, but this method requires two sensors, i.e., a sensor for detecting the packaging material and a sensor for detecting the hot melt.